"Unfortunately Lisa Robin Kelly passed away last evening," Kelly's agent, Craig Wyckoff, said in a statement. "Lisa had voluntarily checked herself into a treatment facility early this week where she was battling the addiction problems that have plagued her these past few years.

"I spoke to her on Monday and she was hopeful and confident, looking forward to putting this part of her life behind her. Last night she lost the battle. Cause of death has not been issued yet and no death certificate has been issued either."

Sources told TMZ that Kelly's new boyfriend took her to rehab earlier this week, but it was too late — the actress suffered a fatal cardiac arrest Wednesday night.

Kelly was a veteran actress who got her start in 1992 on "Married… With Children." Her credits included "Murphy Brown," "Charmed," and "Silk Stockings."

On "That '70s Show," the veteran actress played the promiscuous elder sister of Topher Grace's Eric Forman for five years. Her character was written out, though Kelly returned for a few episodes in Season 5. Then, she was replaced by Christina Moore in Season 6.

Watch a clip of Kelly as Laurie on "That '70s Show":

She told ABC News that her drinking problems stemmed from a miscarriage. "I had lost a baby," she said. "As a result of that, I lost it. I lost everything and I was abusing alcohol."

Alcoholism plagued Kelly for years after that. In 2010, she was charged with a DUI and served probation. Last year, she was arrested for domestic violence against ex-boyfriend John Michas, though she denied the charges and they were eventually dropped.

Last November, both Kelly and her now-estranged husband Robert Gilliam were arrested for assault after a domestic disturbance. Gilliam was convicted of domestic battery and sentenced to three years of probation. And just a few months ago, in June, Kelly was arrested for another DUI.